Wild bees (hymenoptera, apoidea, anthophila) and flowers: evaluation of visit frequencies in urban nature reserves in Rome

Wild bees are among the key organisms sustaining ecosystem functioning. They are highly efficient pollinators whose diversity is strongly influenced by the availability and traits of flowering plants, also in urban ecosystems. We investigated plant-pollinator interactions in the nature reserves of the RomaNatura network in Rome (Italy), focusing on visitation frequencies of wild bee species on spontaneous flora. We analysed associations between bee and plant taxa at the family and genus ranks, as well as relationships between functional traits of bees (ligula length and scopa position) and flowers (inflorescence type, corolla morphology, and flower colour). We recorded 2,139 interactions between 82 spontaneous plant species and 208 wild bee species. Significant associations emerged between bee and plant families and genera, revealing non-random visitation patterns and clear floral preferences across taxonomic levels. Among plants, some groups contribute disproportionately more than others to supporting the wild bee communities. Asteraceae are the most represented and visited by bees and, together with Apiaceae, Brassicaceae, and Boraginaceae, make a major contribution to supporting the wild bee community. Overall, the most attractive morpho-functional traits were calatis, racemose, compound umbel and scorpioid inflorescences; ligulate, tubular, star-shaped and cruciform corollas; yellow/orange, blue/violet/light blue, pink/red/purple, white colouration. Network analyses indicated varying degrees of connectivity, with some bee genera displaying strong specialisation. Functional trait analyses highlighted structured relationships between bee morphology and floral traits: Bees with short-ligula showed a higher level of specialisation, visiting fewer corolla types than bees with long-ligula. No clear relationships emerged between scopa position of bees and corolla type. This study describes the structure of pollination interaction networks in large urban green areas and demonstrates how functional traits of bees and plants shape these networks. The findings provide insights relevant for management strategies aimed at enhancing habitat suitability and supporting pollinator diversity in urban ecosystems.